package com.ctbri.concurrency;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Random;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

public class ReaderWriterList<T> {
	private ArrayList<T> lockedList;
	private ReentrantReadWriteLock lock = new ReentrantReadWriteLock(true);
	
	public ReaderWriterList(int size, T initialValue) {
		lockedList = new ArrayList<>(Collections.nCopies(size, initialValue));
	}
	
	public T set(int index, T element) {
		Lock wlock = lock.writeLock();
		wlock.lock();
		try {
			return lockedList.set(index, element);
		} finally {
			wlock.unlock();
		}
	}
	
	public T get(int index) {
		Lock rLock = lock.readLock();
		rLock.lock();
		try {
			if(lock.getReadLockCount() > 1) 
				System.out.println(lock.getReadLockCount());
			return lockedList.get(index);
		} finally {
			rLock.unlock();
		}
	}
	public static void main(String[] args) {
		new ReaderWriterListTest(30,1);
	}
}

class ReaderWriterListTest {
	  ExecutorService exec = Executors.newCachedThreadPool();
	  private final static int SIZE = 100;
	  private static Random rand = new Random(47);
	  private ReaderWriterList<Integer> list =
	    new ReaderWriterList<Integer>(SIZE, 0);
	  private class Writer implements Runnable {
	    public void run() {
	      try {
	        for(int i = 0; i < 20; i++) { // 2 second test
	          list.set(i, rand.nextInt());
	          TimeUnit.MILLISECONDS.sleep(100);
	        }
	      } catch(InterruptedException e) {
	        // Acceptable way to exit
	      }
	      System.out.println("Writer finished, shutting down");
	      exec.shutdownNow();
	    }
	  }
	  private class Reader implements Runnable {
	    public void run() {
	      try {
	        while(!Thread.interrupted()) {
	          for(int i = 0; i < SIZE; i++) {
	            list.get(i);
	            TimeUnit.MILLISECONDS.sleep(1);
	          }
	        }
	      } catch(InterruptedException e) {
	        // Acceptable way to exit
	      }
	    }
	  }
	  public ReaderWriterListTest(int readers, int writers) {
	    for(int i = 0; i < readers; i++)
	      exec.execute(new Reader());
	    for(int i = 0; i < writers; i++)
	      exec.execute(new Writer());
	  }
	}
